1. Field of the Invention
The invention relates to a zoom lens and a photographing apparatus.
2. Description of the Related Art
An optical imaging system of a photographing apparatus such as a security camera, a video camera, a digital still camera, or a broadcasting camera may use a 4-group zoom lens as a high-quality and high-powered zoom lens.
A 4-group zoom lens includes, from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. In the 4-group zoom lens, zooming is performed by shifting the second lens group in an optical axis direction, and focusing is performed and a variation in an image plane caused by the zooming is compensated by shifting the fourth lens group in the optical axis direction.
However, in a zoom lens having a large zoom ratio, because an angle of view is reduced at a telephoto position, significant image blur may be caused even by a small amount of camera shake. Accordingly, a photographing apparatus may include a camera shake compensating function for compensating for an image blur caused by a camera shake.
The camera shake compensating function may use an optical camera shake compensating method. This method may include a method of shifting some lenses of a lens system in a direction perpendicular to an optical axis direction, or a method using a variable vertical angle prism by varying a vertical angle of a prism disposed at a side of a lens system toward an object side.
In the variable vertical angle prism method, because a prism is disposed closer to an object side than a first lens group that is the largest lens group in a lens system, if a driving system for varying a vertical angle of the prism is also considered, the size of an object side portion of a lens barrel may be increased, and thus a compact size may not be easily achieved.
Meanwhile, in the lens shifting method, in cooperation with a detection system for detecting a camera shake, a control system for applying an amount of compensation with respect to a position of a lens based on a signal output from the detection system, and a driving system for shifting the lens in a direction perpendicular to an optical axis direction based on a signal output from the control system, an image blur caused by a camera shake occurring when, for example, a shutter release button is pressed may be compensated by shifting the lens.
Also, in the lens shifting method, an image blur may be compensated by shifting all or some lenses of a third lens group disposed adjacent to an aperture stop in a direction perpendicular to an optical axis direction. Because the third lens group is fixed in the optical axis direction, a driving system larger than a lens system in a diameter direction may be fixed in the optical axis direction, and thus the size of a whole system may be reduced.
However, an optical system using the lens shifting method has a problem in balance between obtaining a compact size and obtaining a high performance.